The development of nano/micromotors is a research area of intense activity due to numerous potential applications.1-8 While considerable attention has been given to catalytic motors that exhibit self-propulsion in the presence of a hydrogen peroxide fuel, many practical applications would require elimination of the need of chemical fuel.9-15 Several groups have thus explored fuel-free propulsion mechanisms based on externally applied magnetic or ultrasound fields.16-20 The increased capabilities and sophistication of these tiny fuel-free motors hold considerable promise for directed drug delivery, biopsy, cleaning clogged arteries, precision nanosurgery, and localized diagnosis in hard-to-reach places, for example. To fulfill these exciting potential applications, particular attention is drawn to the biocompatibility of the motors in biological environments and to their performance in undiluted biological media. The metallic or polymeric components of common artificial nano/micromotors are facing destructive immune attack once entering into the bloodstream due to the foreign nature of these materials.
Natural cells and their derivatives are highly optimized by nature for their unique in vivo functions and possess attractive features desired for systemic cargo delivery.21-23 As a result, various types of cells, such as red blood cells (RBCs, also referred to as erythrocytes), white blood cells, macrophages, engineered stem cells and so on, have been employed to carry and deliver therapeutic or imaging agents.24,25 The intrinsic properties of these natural carriers have opened the door to creative cargo delivery strategies and novel biomaterials development. Among these cell-based carriers, RBCs are of particular interest owing to their vast availability, unique mechanical attribute, surface immunosuppressive property, and versatile cargo-carrying capability.26-28 As such, numerous RBCs based or inspired delivery systems have been recently developed for cargo delivery, relying on the prolonged transport property of RBCs in the bloodstream.29-32 However, there are no reports on how to bestow active propulsion force upon the passively moving RBCs, and thus to utilize the cells as a powerful autonomous micromotor.
Several groups have demonstrated the capability of synthetic micro/nanoscale motors for guided transport of drug-loaded nanoparticles and capture and transport of cells. However, the ability to transport diagnostic imaging agents and therapeutic drugs at the same time within a single powered motor, without affecting the propulsion and direction of the motor, has not yet been demonstrated. Such multicargo-loaded motors would provide an attractive delivery vehicle for the concurrent imaging and treatment of diseases.